TECHNICAL FILED
[0001] The present invention relates to a method of producing a semiconductor wafer. More
particularly, it relates to a method of producing a semiconductor wafer, which comprises
applying a semiconductor wafer surface protecting adhesive tape having heat shrinkability
to the surface on which an integrated circuit of a semiconductor wafer such as silicon
wafer is mounted (hereinafter referred to as the wafer surface), supplying the semiconductor
wafer to a machine for grinding the back surface of the semiconductor wafer, grinding
the surface on which the integrated circuit of the semiconductor wafer is not mounted
(hereinafter referred to as the wafer back surface) and heating the adhesive tape
in the grinding machine, thereby peeling off the adhesive tape from the wafer surface.
BACKGROUND ART
[0002] A semiconductor integrated circuit (hereinafter referred to as IC) is usually produced
by slicing a high purity silicon single crystal to form a semiconductor wafer, mounting
an integrated circuit on the surface using a means such as etching, shaving the back
surface of the semiconductor wafer by grinding, etching, lapping or the like, thereby
to reduce the thickness to about 200 to 400 µm, and dicing the wafer to form a chip.
To sum up, after the completion of formation of IC, a chip is formed in a dicing step
after going through four steps, that is, a step of applying an adhesive tape to the
semiconductor wafer surface, a step of grinding the back surface of the semiconductor
wafer, a step of peeling off the adhesive tape, and a step of washing the semiconductor
wafer surface. When the semiconductor wafer is fed between these production steps,
the semiconductor wafer is usually fed in the state of being encased in a cassette.
That is, in the respective steps, a unit operation of taking out from the cassette
and encasing it into the cassette is repeated. Such an operation can be not only the
larger cause of breakage of a wafer because of the recent tendency of a reduction
in thickness of the layer and an increase in diameter, but also the cause of complication
of the steps and loss of the working time.
[0003] With the reduction in size of a semiconductor chip, a tendency of a reduction in
thickness of a wafer is increased and a conventional thickness (about 200 to 400 µm)
of a wafer after grinding the back surface was reduced to about 150 µm, depending
on the kind of the chip. Also regarding the size, a conventional diameter (maximum
8 inch) tends to be increased to 12 inch, furthermore to 16 inch. Under the circumstance
of the reduction in thickness and increase in diameter of the semiconductor wafer,
the semiconductor wafer grinded the back surface is liable to cause warp. In case
that the adhesive tape is applied on the surface of the wafer, its tendency is increased
by a tension of the adhesive tape. For the reason, the semiconductor wafer whose thickness
is reduced after grinding contacts with a encasing port of the cassette in case of
containing in the cassette and, therefore, the semiconductor wafer is liable to be
broken only by applying a small impact.
[0004] In the grinding step of the back surface of the semiconductor wafer, a wafer surface
protecting adhesive tape is applied on the wafer surface for the purpose of protecting
IC formed on the surface of the semiconductor wafer and preventing the semiconductor
wafer from breaking by a grinding stress. Since the adhesive tape becomes unnecessary
after the completion of the grinding of the wafer back surface, it is peeled off from
the wafer surface by using an adhesive tape peeling device. As a peeling method, for
example, Japanese Patent Kokai Publication No. 28950/1990 discloses a method of applying
a tape having a strong adhesive force referred to as a release tape on the base film
surface of an adhesive tape applied on the semiconductor wafer surface and peeling
the adhesive tape via the release tape. However, under the circumstance of the reduction
in thickness and increase in diameter of the semiconductor wafer, the semiconductor
is liable to be broken when the semiconductor wafer with severe warp is fixed to a
chuck table of a peeling device or the adhesive tape is peeled off from the semiconductor
wafer, as described above.
[0005] To prevent the breakage of the wafer when the adhesive tape is peeled off from the
semiconductor wafer surface, there is suggested a film for surface protection wherein
the peelability is improved. For example, Japanese Patent Kokai Publication No. 189938/1985
describes a method of applying an adhesive film comprising a light transmitting substrate
and a pressure-sensitive adhesive having a property capable of curing by light irradiation
to form a three-dimensional network, said pressure-sensitive adhesive being provided
on said substrate, on the wafer surface in case of grinding the back surface of the
semiconductor wafer, irradiating this adhesive film with light after grinding, and
peeling off the adhesive film without causing the breakage of the wafer. However,
the pressure-sensitive adhesive (adhesive layer) having a property capable of curing
by light irradiation to form a three-dimensional network, which is disclosed in the
invention, is an adhesive layer capable of polymerizing by the radical polymerization.
Therefore, when oxygen is entrapped between the wafer and adhesive layer, the curing
reaction does not proceed sufficiently by the polymerization inhibition effect of
oxygen and the wafer surface is sometimes contaminated with the uncured adhesive having
a low cohesive force at the time of peeling after grinding the wafer back surface.
Since the wafer surface on which an integrated circuit is mounted has a complicated
irregularity, it is very difficult to apply the adhesive film without entrapping any
air (oxygen). To make a system wherein oxygen is removed for applying, it is necessary
to newly dispose a device. Contamination caused by such an adhesive can be removed
by washing with a solvent, sometimes, but can not completely be removed at present
in almost all of cases. According to this method, any advantage can not be found out
with respect to the prevention of the breakage of the wafer and reduction of the working
time when the wafer is fed to the adhesive tape peeling step after grinding the wafer
back surface.
[0006] As described above, there has been required a method of producing a semiconductor
wafer, which can maintain the contamination resistance of the wafer surface and prevention
of the breakage of the wafer back surface at the time of grinding at the same level
as that of the prior art under the circumstance of the increase in bore diameter and
reduction in thickness of the semiconductor wafer, and does not cause the breakage
of the wafer when the adhesive tape is peeled off and the wafer is fed between the
respective processing steps, and also which can reduce the working time.
DISCLOSURE OF THE INVENTION
[0007] It is an object of the present invention to solve the above problems and to provide
a method of producing a semiconductor wafer, which can prevent the breakage of the
wafer when the semiconductor wafer is fed and the adhesive tape for semiconductor
wafer surface protection is peeled off, and which can reduce the working time.
[0008] To accomplish the above object, the present inventors have intensively studied. As
a result, they have found that an adhesive tape can be easily peeled off without causing
the breakage of a semiconductor wafer by applying an adhesive tape for semiconductor
wafer surface protection having heat shrinkability on the wafer surface, grinding
the back surface in a semiconductor wafer back surface grinding machine and heating
the adhesive tape in the same grinding machine, thereby making it possible to omit
an adhesive tape peeling step as a conventional subsequent step. Thus, the present
invention has been completed.
[0009] That is, the present invention provides a method of producing a semiconductor wafer
wherein an adhesive tape is applied on the surface of the semiconductor wafer and,
after grinding the back surface of the semiconductor wafer using a grinding machine,
the adhesive tape is peeled off, said process comprises using an adhesive tape having
heat shrinkability as the adhesive tape, grinding the back surface of the semiconductor
wafer and heating the adhesive tape in the grinding machine, thereby peeling off the
adhesive tape from the surface of the semiconductor wafer in the grinding machine.
[0010] In the present invention, a preferable method of heating the adhesive tape in the
grinding machine includes, for example, a method using at least one heating medium
selected from the group consisting of warm water and warm air. The temperature of
the heating medium is within a range from 50 to 99°C, and preferably from 50 to 80°C.
Furthermore, the wafer surface may also be washed with a washing solution after the
adhesive tape was peeled off in the grinding machine. In this case, water, warm water
or the like is preferably used as the washing solution.
[0011] According to the method of the present invention, even if the back surface of the
semiconductor wafer having a diameter of 6 to 16 inch, preferably 6 to 12 inch, is
ground, thereby to reduce the thickness to about 80 to 400 µm, preferably 80 to 200
µm, the semiconductor wafer is not broken when the adhesive tape is peeled off after
grinding the back surface. Since the method is a method of peeling off the adhesive
tape by utilizing heat shrinkability of the adhesive tape itself in the grinding machine
after grinding the back surface, the adhesive tape is not applied on the surface of
the wafer in case that the wafer is taken out from the grinding machine and encased
in the cassette, resulting in little warp. Accordingly, the wafer is not broken by
contacting with the encased port of the cassette in case of encased in the cassette.
Furthermore, feed to the washing step as the subsequent step can be omitted if the
wafer surface is washed in the grinding machine.
[0012] According to the present invention, the semiconductor wafer is not broken in case
of peeling off the adhesive tape even in case that the back surface of the semiconductor
wafer having a diameter of 6 to 16 inch is ground, thereby to reduce the thickness
to about 80 to 200 µm. Since a method of peeling the adhesive tape by utilizing heat
shrinkability in the grinding machine, the wafer cause little warp when the wafer
is taken out from the grinding machine and encased in the cassette. Accordingly, the
wafer is not broken by contacting with the encasing port of the cassette in case of
encase in the cassette. Furthermore, a washing step, which has conventionally been
performed as the subsequent step, can be omitted if the adhesive tape is heated and
peeled off in the grinding machine by using warm water as the heating medium of the
adhesive tape and, furthermore, the wafer is washed with a washing solution. Therefore,
according to the present invention, a series of steps from grinding of the back surface
of the semiconductor wafer to washing of the wafer surface can be carried out in a
short time, thereby making it possible to reduce the working time.
BEST MODE FOR CARRYING OUT THE INVENTION
[0013] The present invention will be described in detail hereinafter. The summary of the
present invention is as follows. That is, a release film is peeled off from an adhesive
layer of an adhesive tape for surface protection of a semiconductor wafer (hereinafter
referred to as an adhesive tape), thereby exposing the adhesive layer surface, and
then the adhesive tape is applied on the surface, on which an integrated circuit of
the semiconductor wafer is mounted, via the adhesive layer. Then, the semiconductor
wafer is fixed to a chuck table of a grinding machine via a base film layer of the
adhesive tape and the back surface of the semiconductor wafer is ground. After the
completion of grinding, the adhesive tape is subsequently heated in the grinding machine,
thereby peeling off the adhesive tape. Then, the wafer surface is optionally washed,
taken out from the grinding machine and contained in a cassette. The cassette is fed
to the subsequent step such as dicing step.
[0014] The adhesive tape used in the present invention is an adhesive tape wherein an adhesive
layer is formed on one surface of a base film having heat shrinkability. To protect
the adhesive layer during the storage and feed, a release film usually referred to
as a separator is preferably applied on the surface of the adhesive layer.
[0015] Regarding the method of producing the adhesive tape, an adhesive is first applied
on one surface of a release film and dried to form an adhesive layer, and then the
adhesive layer is transferred to the surface of a base film having heat shrinkability.
As the base film having heat shrinkability, preferred are those wherein a shrikage
factor at 50 to 99°C, preferably 50 to 80°C, in a monoaxial or biaxial (longitudinal,
transverse) direction is within a range from 5 to 50%.
[0016] The release film may be essentially any film having a surface tension lower than
that of the base film even if the absolute value of a surface tension is any value.
The heat resistance of the release film exerts an influence on dryness of the adhesive
applied on the surface. When the heat resistance is poor, it is necessary to adjust
the drying temperature of the adhesive to a low temperature. Therefore, it takes a
long time to dry the adhesive and the adhesive can not be efficiently dried in a short
time. For example, the release film causes heat shrinkage in a drying oven and defects
such as wrinkle occur in the release film and, therefore, an adhesive layer having
a uniform thickness can not be formed, sometimes. From such a point of view, the release
film preferably has the predetermined heat resistance. As the evaluation criteria
of the heat resistance, it preferably has a Vicat softening point of not less than
100°C. As far as the above conditions are satisfied, the release film is not specifically
limited. The release film may be a single-layer film or a multi-layer film, and can
be appropriately selected from commercially available products.
[0017] Specific examples of the release film include films produced from high-density polyethylene,
polypropylene, polyethylene terephthalate, polyamide resin, or a mixture thereof.
Preferred examples thereof include high-density polyethylene film, polypropylene film
and polyethylene terephthalate film. The method of producing these films is not specifically
limited, and these films may be those produced by publicly known methods such as extrusion
method, calendering method and the like. The molding temperature may be a temperature
which is not less than a glass transition point or a softening point of the raw resin
and is lower than a decomposition temperature.
[0018] For the purpose of reducing a peeling stress when the release film is peeled from
the adhesive layer, a releasant such as silicon compound may be applied on the surface
of the release film, on which the adhesive is applied, as far as the adhesive layer
is not contaminated. The thickness of the release film varies depending on the drying
conditions, kind and thickness of the adhesive layer, or processing conditions and
processing method of the adhesive tape, but is usually from 10 to 1000 µm, and preferably
from 20 to 100 µm.
[0019] The heat shrinkability of the adhesive tape exerts an influence on the peelability
of the adhesive tape from the semiconductor wafer surface. When the shrinkage factor
is too low, poor peel occurs at the time of heating and it takes a long time to peel
the adhesive tape. On the other hand, when the shrinkage factor is too high, the adhesive
tapes is deformed with a lapse of tine during the storage and, therefore, the workability
in case of applying the adhesive tape on the wafer surface is lowered. From such a
point of view, the heat shrinkage factor at 50 to 99°C, preferably 50 to 80°C, is
preferably from 5 to 50%. In this case, the adhesive tape may be a tape which exhibits
the above heat shrinkability in at least one point within the above temperature range.
The shrinkage direction may be a monoaxial direction or a biaxial (longitudinal, transverse)
direction. The material is not specifically limited. Specific examples thereof include
ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, polybutadiene
copolymer, polybutadiene, soft vinyl chloride resin, resins such as polyolefin, polyester,
polyamide and ionomer, and copolymer elastomer thereof, and diene, nitrile and acrylic
films. The base film may be an single-layer material or a multi-layer material.
[0020] Taking the prevention of the breakage of the semiconductor wafer during the grinding
of the wafer back surface into consideration, a film having elasticity obtained by
forming a resin having a Shore D-scale hardness of 40 or less defined in ASTM-D-2240
into a film, for example, ethylene-vinyl acetate copolymer (hereinafter referred to
as EVA) film and polybutadiene film may be preferably used. In this case, it is preferred
to laminate a film having both a hardness higher than that of the base film, and a
heat shrinkablity on the surface opposite the surface on which the adhesive layer
of the base film is provided, for example, a film obtained by forming a resin having
a Shore D-scale hardness of higher than 40 into a film. Consequently, the rigidity
of the adhesive tape is increased, thereby improving the applying workability.
[0021] The thickness of the base film is appropriately decided according to the shape, surface
condition, grinding method and grinding conditions of the semiconductor wafer to be
protected, or cutting and applying workability of the adhesive tape for wafer surface
protection. Usually, thickness of the base film is from 10 to 1000 µm, preferably
from 100 to 300 µm.
[0022] The method of producing the base film is not specifically limited, and the base film
may be any one produced by publicly known methods such as extrusion method and calendering
method. The molding temperature may be a temperature which is not less than a glass
transition point or a softening point of the raw resin and is lower than a decomposition
temperature. To impart the heat shrinkability to the base film, stretching is preferably
performed at least in a monoaxial direction. The stretching ratio exerts an influence
on the peelability and workability in case that the adhesive tape is peeled off from
the wafer surface after grinding the wafer back surface. When the stretching ratio
is low, sufficient shrinkage of the base film does not occur by heating in case of
peeling from the wafer surface, resulting in deterioration of the peelability and
workability. Taking such a point into consideration, the stretching ratio is not less
than 1.2, and preferably not less than 1.5. The stretching of the base film may be
a monoaxial stretching wherein stretching is performed in a longitudinal or transverse
direction of the film, or a biaxial stretching wherein stretching is performed in
a longitudinal and transverse direction of the film. The upper limit of the stretching
ratio is about 10 taking the breakage at the time of stretching into consideration.
[0023] Also the stretching method is not specifically limited, and may be publicly known
methods such as longitudinal monoaxial stretching method using a roll rolling method
and roll stretching method, longitudinal/transverse successive biaxial stretching
method using a tenter, and longitudinal/transverse simultaneous biaxial stretching
method using a tenter. The stretching temperature is preferably from 40 to 70°C. The
base film stretched as described above is heat-treated so as not to cause shrinkage
with a lapse of time. The heat treating temperature is preferably from 45 to 80°C.
[0024] It is necessary that a surface tension of the surface of the base film, on which
at least an adhesive layer is to be applied, is higher than that of the release film.
The base film may be any film having a surface tension higher than that of the release
film even if the absolute value of a surface tension is any value. Taking the adhesion
of the adhesive layer to base film after transferring from the release film into consideration,
the base film may be preferably selected according to such criteria that the film
is a stretched film having a surface tension of not less than 35 dyne/cm. When the
surface tension is low, the adhesion between the adhesive layer and the base film
is lowered and transfer of the adhesive layer from the release film can not be performed,
satisfactorily. The method of increasing the surface tension of the base film includes,
for example, corona discharge treatment.
[0025] The composition of the adhesive is not specifically limited, and can be appropriately
selected from commercially available products. In view of the adhesion, applicability
and contamination resistance of the wafer surface, an acrylic adhesive is preferred.
Such an acrylic adhesive can be obtained by copolymerizing a monomer mixture containing
an alkyl acrylate monomer and a monomer having a carboxyl group. If necessary, it
is possible to copolymerize with a vinyl monomer, a polyfunctional monomer and an
internal crosslinking monomer, which are copolymerizable with them.
[0026] The alkyl acrylate monomer includes, for example, methyl acrylate, methyl methacrylate,
ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate,
butyl methacrylate, hexyl acrylate, hexyl methacrylate, octyl acrylate, octyl methacrylate,
nonyl acrylate, nonyl methacrylate, dodecyl acrylate and dodecyl methacrylate. A side
chain alkyl group of these monomers may be in a straight-chain or branched form. Two
or more alkyl acrylate monomers may be used in combination.
[0027] The monomer having a carboxyl group includes, for example, acrylic acid, methacrylic
acid, crotonic acid, itaconic acid, maleic acid and fumaric acid. The vinyl monomer
copolymerizable with the alkyl acrylate monomer and the monomer having a carboxyl
group includes, for example, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl
acrylate, hydroxypropyl methacrylate, acrylamide, methacrylamide, dimethylamino acrylate,
dimethylamino methacrylate, vinyl acetate, styrene and acrylonitrile.
[0028] The polymerization reaction mechanism of the adhesive polymer include, for example,
radical polymerization, anionic polymerization and cationic polymerization. Taking
the production cost of the adhesive, influence of a functional group of the monomer,
and influence of an ion on the semiconductor wafer surface into consideration, the
adhesive polymer is preferably polymerized by the radical polymerization. A radical
polymerization initiator used in case of polymerizing by the radical polymerization
includes, for example, organic peroxides such as benzoyl peroxide, acetyl peroxide,
isobutyryl peroxide, octanoyl peroxide, ditertial butyl peroxide and ditertial peroxide;
inorganic peroxides such as ammonium persulfate, potassium persulfate and sodium persulfate;
and azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile
and 4,4'-azobis-4-cyanovaleric acid.
[0029] In case of polymerizing by the emulsion polymerization, inorganic peroxides such
as water-soluble ammonium persulfate, potassium persulfate and sodium persulfate;
and azo compounds having a carboxyl group in the molecule, such as water-soluble 4,4'-azobis-4-cyanovaleric
acid are preferred among these radical polymerization initiators. Taking an influence
of an ion on the semiconductor wafer surface into consideration, an azo compound having
a carboxyl group in the molecule, such as water-soluble 4,4'-azobis-4-cyanovaleric
acid is more preferred.
[0030] A crosslinking agent having two or more crosslinking functional groups in one molecule
used in the present invention is used to adjust an adhesive force and a cohesive force
by reacting with a functional group of the adhesive polymer. The crosslinking agent
includes, for example, epoxy compounds such as sorbitol polyglycidyl ether, polyglycerol
polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether,
glycerol polyglycidyl ether, neopentyl glycol diglycidyl ether and resorcin diglycidyl
ether; isocyanate compounds such as tetramethylene diisocyanate, hexamethylene diisocyanate,
toluene diisocyanate triadduct of trimethylolpropane and polyisocyanate; aziridine
compounds such as trimethylolpropane-tri-β-aziridinyl propionate, tetramethylolmethane-tri-β-aziridinyl
propionate, N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxyamide), N,N'-hexamethylene-1,6-bis(1-aziridinecarboxyamide),
N,N'-toluene-2,4-bis(1-aziridinecarboxyamide) and trimethylolpropane-tri-β-(2-methylaziridine)propionate;
and melamine compounds such as hexamethoxymethylolmelamine.
[0031] These compounds may be used alone, or two or more kinds of them may be used in combination.
In case of using the epoxy crosslinking agent among the above crosslinking agents,
the rate of the crosslinking reaction is low. In case that the reaction does not proceed
sufficiently, the cohesive force of the adhesive layer is lowered and contamination
caused by the adhesive layer occurs depending on the irregularity of the semiconductor
wafer surface. Accordingly, it is preferred to appropriately add a catalyst such as
amine or to copolymerize a monomer containing an amine functional group having an
catalytic action with the adhesive monomer, or to use an aziridine crosslinking agent
having a property as amine in combination in case of using the crosslinking agent.
[0032] The amount of the crosslinking agent is usually added within a range where the number
of functional groups in the crosslinking agent is not larger than that in the adhesive
polymer. However, when a functional group is newly formed by the crosslinking reaction
and the crosslinking reaction proceeds slowly, excess crosslinking agent may be added,
if necessary. The adhesive force of the adhesive tape for grinding the wafer back
surface is usually from about 10 to 1000 g/25 mm, and preferably from about 30 to
600 g/25 mm, in terms of an adhesive force to a SUS-BA plate. The adhesive force is
adjusted within the above range according to the grinding conditions of the wafer
back surface, bore diameter of the wafer, and thickness of the wafer after grinding.
Specifically, the crosslinking agent is added in the amount within a range from 0.1
to 30 parts by weight, and preferably from 0.3 to 15 parts by weight, based on 100
parts by weight of the adhesive polymer.
[0033] It is also possible to optionally add a surfactant to the adhesive as far as the
wafer surface is nit contaminated. The surfactant to be added may be nonionic or anionic
as far as the wafer surface is not contaminated. Examples of the nonionic surfactant
include polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether and
polyoxyethylene lauryl ether. Examples of the anionic surfactant include alkyl diphenyl
ether disulfonate and its salt, bisnaphthalene sulfonate and its salt, polyoxyalkyl
sulfosuccinate and its salt, and sulfate of polyoxyethylene phenyl ether and its salt.
[0034] The above surfactants may be used alone, or two or more kinds of them may be used
in combination. The amount of the surfactant is preferably from 0.05 to 5 parts by
weight, and more preferably from 0.05 to 3 parts by weight, based on the total weight
of the adhesive polymer and crosslinking agent, that is, 100 parts by weight of the
crosslinked adhesive polymer.
[0035] As a method of coating an adhesive coating emulsion or solution on one surface of
the base film or release film, there can be used a conventionally known coating method,
for example, roll coating method, gravure coating method and bar coating method. The
drying conditions of the applied adhesive are not specifically limited. In general,
it is preferred to dry at a temperature ranging from 80 to 200°C for 10 seconds to
10 minutes. More preferably, drying is performed at a temperature ranging from 80
to 170°C for 15 seconds to 5 minutes. The thickness of the adhesive layer is appropriately
decided according to the surface condition, shape and grinding method of the back
surface of the semiconductor wafer, but is usually from about 2 to 100 µm, and preferably
from 5 to 70 µm, taking the adhesive force in case of grinding the back surface of
the semiconductor wafer and the peelability after the completion of the grinding into
consideration.
[0036] After the adhesive layer was formed on the surface of the release film as described
above, the base film is put on the surface of the adhesive layer and the adhesive
layer is transferred to the surface of the base film by pressing. The transferring
method may be a publicly known method. For example, there can be used a method of
putting the surface of the base film to the surface of the adhesive layer formed on
the surface of the release film, and pressing them by passing through a nip roll.
The release film is preferably peeled off from the surface of the adhesive layer immediately
before using as the adhesive tape. The adhesive tape thus obtained is formed into
a roll or cut into a predetermined shape, and then stored or fed.
[0037] The method of producing the semiconductor wafer, comprising a series of steps from
the step of adhering the adhesive tape on the surface of the semiconductor wafer to
the dicing step will be described in detail hereinafter.
[0038] In the present invention, the adhesive tape is applied on the semiconductor wafer
surface via the adhesive layer. The operation of applying the adhesive film on the
semiconductor wafer surface is sometimes performed by human hands, but is usually
performed by using a device referred to as an automatic applying device equipped with
an adhesive film in the form of a roll. Such an automatic applying device includes,
for example, Model ATM-1000B and ATM-1100 (manufactured by Takatori Corp.) and Model
STL series (manufactured by Teikoku Seiki Co., Ltd.).
[0039] The semiconductor wafer is fixed to the chuck table of the wafer back surface grinding
machine via the base film layer of the adhesive tape. The semiconductor wafer is ground
by using the grinding machine until the thickness of the wafer back surface is reduced
to a predetermined thickness. During the grinding, cooling water is generally poured
on the grinding surface. As a back surface grinding system, a publicly known grinding
system such as through-feed system and infeed system is employed. The thickness of
the semiconductor is from 500 to 1000 µm before grinding, whereas, the thickness is
from about 80 to 400 µm, and preferably from about 80 to 200 µm after grinding. The
thickness of the semiconductor wafer before grinding is appropriately decided by the
bore diameter and kind of the wafer, whereas, the thickness of the semiconductor wafer
after grinding is appropriately decided by the size of the resulting chip and the
kind of IC.
[0040] After the completion of the grinding, shavings were removed by a method of pouring
pure water on the grinding surface. Then, the wafer was turned over and fixed to the
chuck table via the wafer back surface. The adhesive tape is then heated to cause
shrinkage of the base film layer, thereby peeling off the adhesive tape from the wafer
surface. The peeled adhesive tape is removed out of the system by a method of sucking
using an exclusive jig.
[0041] The state where the adhesive tape is peeled off refers to the state where the adhesive
tape applied on the wafer surface is peeled off over not less than 20% of the wafer
surface. In this case, the other portion of the heated adhesive tape is deformed by
heat shrinkage and is in the state of being easily peeled off. Although the detailed
peeling mechanism is not clear, in case of peeling with heating using warm water,
warm water penetrates almost all of the interface between the wafer surface and adhesive
layer even in the non-peeled portion. Also in case of peeling by using a warm air,
partial lifting attended by a deformation stress of the base film occurs at the interface
between the wafer surface and adhesive layer.
[0042] The heating method is not specifically limited as far as the adhesive tape applied
on the wafer surface can cause heat shrinkage, and includes, for example, a method
of pouring warm water at 50 to 99°C, preferably 50 to 80°C, on the adhesive tape,
a method of contacting the adhesive tape with water at 50 to 99°C, preferably 50 to
80°C, by using a method of immersing in warm water at 50 to 99°C, preferably 50 to
80°C, together with the wafer, and a method of blowing a warm air at 50 to 99°C, preferably
50 to 80°C. Taking the heat conductivity to the adhesive tape for causing shrinkage
of the base film into consideration, a method of contacting warm water at 50 to 99°C,
preferably 50 to 80°C, with the adhesive tape is preferred. Furthermore, considering
the fact that the wafer surface is washed in the same grinding machine after peeling
off the adhesive tape, a method of heating by pouring warm water at the above temperature
on the adhesive tape surface is preferred. In this case, considering the fact that
the peelability is more improved by uniformly pouring warm water on the base film
surface of the adhesive tape, a method of pouring warm water with rotating the wafer
at a rotational speed of 5 to 500 rpm is preferred. Regarding the rotating, method
of the wafer, the wafer may be rotated on the center of the wafer as a rotation center
point.
[0043] In the present invention, after peeling the adhesive tape the wafer surface can be
washed by pouring a washing liquid such as pure water, alcohols thereon. Pure water
is preferably used as the washing liquid. By using these methods, an exclusive washing
step to be carried out after the wafer back surface grinding step can be usually omitted
and a series of steps from the wafer back surface grinding step to the surface washing
step can be simplified, thereby making it possible to reduce the working time.
[0044] The heating temperature can be appropriately selected within a range from 50 to 99°C,
and preferably from 50 to 80°C, according to the stretching ratio of the base film,
adhesive force of the tape for semiconductor wafer surface protection, and the kind
of the heating method. The heating time also exerts an influence on the peelability
from the semiconductor wafer surface. The heating time varies depending on the stretching
ratio and heating temperature of the base film. Usually, the heating time is from
1 to 60 seconds, and preferably from 10 to 30 seconds, taking the workability into
consideration.
[0045] Conventionally, there has been employed a method of encasing a wafer in a cassette
after the completion of the grinding of the wafer back surface, feeding the cassette
to an adhesive tape peeling step, setting the cassette in a peeling device, taking
out the wafer from the cassette, and peeling the adhesive tape. There has also been
employed a method that peeling off the adhesive tape, then encasing again in the cassette,
feeding the cassette to a washing step, taking out the wafer from the cassette, setting
the wafer in a washing device, and washing the wafer surface. In case of feeding to
the washing step, the wafer is encased into or taken out from the cassette in the
state where the adhesive tape is applied on the wafer surface. Therefore, when the
wafer is largely ground until the thickness of the wafer is reduced to 200 µm or less,
the wafer causes severe warp and is often broken by an impact produced by contacting
the wafer with the encasing port of the cassette. In case that the bore diameter is
large such as 12 inch or more, severe warp occurs even if the thickness after grinding
is about 400 µm.
[0046] On the other hand, according to the method of the present invention, the adhesive
tape is peeled off by heating in the back surface grinding machine and, at the same
time, the washing treatment of the wafer surface is carried out. Therefore, it is
unnecessary that the wafer whose thickness was reduced by grinding the back surface
is encased in the cassette and then fed to the peeling step, furthermore to the washing
step. Therefore, the time of working of encasing into the cassette for wafer feeding
and the time of working of taking out from the cassette are very small. Particularly,
since feed from the back surface grinding step to the peeling step can be omitted,
the breakage of the wafer caused by warp of the wafer at the time of encasing in or
taking out from the cassette can be prevented. Moreover, the wafer surface washing
step can also be omitted by washing the wafer surface with a washing solution such
as pure water, alcohols in the grinding machine after the completion of the back surface
grinding, heating of the adhesive tape and peeling. Finally, a series of steps are
completed by drying the wafer using a method of rotating at a high speed such as about
1000 to 10000 rpm. The size of the semiconductor wafer, to which the present invention
can be applied, is from 6 to 16 inch, and preferably from 6 to 12 inch, in terms of
a diameter.
Examples
[0047] The following Examples further illustrate the present invention in detail but are
not to be construed to limit the scope thereof. Various characteristic values shown
in the Examples were measured by the following procedure.
(1) Shrinkage factor (%) of adhesive tape
[0048] Fifteen test pieces having a square shape of 10 cm in side are made by selecting
each optional position of an adhesive tape. After peeling off a release film from
the test piece, the test piece is heated in an air oven at 25, 50 and 80°C for 1 minute
and then allowed to stand at room temperature for 5 minutes. The length in the longitudinal
direction (machine direction) of the test piece is measured, and then the shrinkage
factor

is determined from the length before heating (L
1) and the length after heating (L
2). Under the respective conditions, the measurement was performed five times and its
average value is determined.
(2) Measurement of wafer surface contamination by using ESCA
[0049] A 8 inch silicon mirror wafer was cut into pieces having a square shape of 1 cm in
side by using a diamond cutter without contaminating the surface. The surface of the
cut wafer was measured under the following conditions by using ESCA to determine a
ratio of carbon to silicon (hereinafter referred to as a ratio C/Si), and then the
contamination state of the silicon wafer is examined.
〈ESCA measurement conditions and method for calculation of ratio C/Si〉
[0050]
X-ray source: MgK α ray (1253.6 eV), X-ray output: 300 W, Measuring vacuum degree:
not more than 2 x 10-7 Pa, C/Si: (peak area of carbon)/(peak area of silicon)
〈Method for evaluation of ratio C/Si〉
[0051] The C/Si value of the silicon mirror wafer before applying a test sample is 0.10
(blank value). Accordingly, it is judged that no contamination is recognized when
the C/Si value of the silicon mirror wafer after applying the test sample is from
about 0.10 to 0.12, whereas, it is judged that contamination is recognized when the
C/Si value exceeds the above range.
(3) Measurement of adhesive force
[0052] A test sample is applied on the surface of a SUS-BA plate having a size of 5 x 20
cm at 23°C via an adhesive layer, and then allowed to stand for 1 hour. The stress,
produced by peeling off the test sample from the SUS-BA plate at a peel angle of 180
degree and a peel rate of 300 mm/min. with holding one end of the test sample, is
measured and then reduced in terms of g/25 mm.
Example 1
[0053] 148 Parts by weight of deionized water, 2 parts by weight (1 part by weight as a
surfactant alone) of an ammonium salt of polyoxyethylene nonyl phenyl ether sulfate
(trade name: Newcol-560SF manufactured by Nippon Nyukazai Co., Ltd., aqueous 50 wt
% solution) as an anionic surfactant, 0.5 parts by weight of 4,4'-azobis-4-cyanovaleric
acid (trade name: ACVA, manufactured by Otsuka Chemistry Co., Ltd.) as a polymerization
initiator, 74 parts by weight of butyl acrylate, 14 parts by weight of methyl methacrylate,
9 parts by weight of 2-hydroxyethyl methacrylate, 2 parts by weight of methacrylic
acid and 1 part by weight of acrylamide are charged in a polymerization reactor and
the emulsion polymerization was carried out at 70°C with stirring for 9 hours to obtain
an aqueous acrylic resin emulsion. This emulsion was neutralized with 14 wt% ammonia
water to obtain an adhesive polymer (chief material) emulsion. 100 Parts by weight
of the resulting adhesive chief material emulsion (concentration of adhesive polymer;
about 40% by weight) was collected and the pH was further adjusted to 9.3 by adding
14 wt% ammonia water. Then, 2 parts by weight of an aziridine crosslinking agent (trade
name: Chemitite PZ-33, manufactured by Nippon Shokubai Co., Ltd.) and 5 parts by weight
of diethylene glycol monobutyl ether as a film-forming auxiliary were added to obtain
an adhesive coating solution.
[0054] Using a polypropylene film having a thickness of 50 µm, a Vicat softening point of
140°C and a surface tension (of one surface) of 30 dyne/cm, formed by the T-die extrusion
method, as a release film, an aqueous acrylic resin emulsion type adhesive obtained
by the above method was applied on one surface of the release film by the roll coater
method, and then dried at 100°C for 60 seconds, thereby providing an acrylic adhesive
layer having a thickness of 10 µm on the surface of the release film.
[0055] An unstretched ethylene-vinyl acetate copolymer (hereinafter referred to as EVA)
film formed by the T-die extrusion method was stretched at 50°C in a stretch ratio
of 3.0 in the longitudinal direction, and then thermally fixed at 60°C to form a monoaxially
stretched EVA film having a thickness of 120 µm. One surface of the monoaxially stretched
EVA film was subjected to a corona discharge treatment, thereby adjusting the surface
tension to 50 dyne/cm, and the resulting film was used as a base film.
[0056] An adhesive tape having an adhesive force of 200 g/25 mm was obtained by putting
the corona discharge-treated surface of the base film to the surface of the acrylic
adhesive layer provided on the release film and pressing at a pressure of 2 kg/cm
2, thereby transferring the adhesive layer to the base film. The heat shrinkage factor
at each temperature of the adhesive tape was measured by the above procedure. The
results are shown in Table 1.
[0057] The resulting adhesive tape was applied on the surface of the fifty mirror wafers
having a diameter of 8 inch and a thickness of 700 µm and the wafers were supplied
to a back surface grinding machine. In the grinding machine, rough grinding, finish
grinding and back surface washing were carried out in order. That is, in the back
surface grinding machine, the mirror wafer was roughly ground at a grinding rate of
300 µm/min., thereby reducing the thickness to 170 µm, and then finish grinding was
carried out at a rate of 20 µm/min, thereby to reduce the thickness to 120 µm. Finally,
the back surface was washed and, after turning over the wafer, warm water at 60°C
was poured on the adhesive tape applied on the wafer surface for 10 seconds. Then,
warm water at 60°C was further poured for 10 seconds with rotating the wafer at 500
rpm, thereby peeling off the adhesive tape. After rotating at 3000 rpm and drying,
the wafer was taken out from the grinding machine and then encased in the cassette.
All of fifty wafers could be encased without causing the breakage. The time required
from the beginning of the grinding to encasing was 150 minutes. The results are shown
in Table 1.
Example 2
[0058] In the same manner as that described in Example 1, except that the adhesive tape
was heated by a warm air at 80°C for 30 seconds after grinding the back surface of
wafer, a semiconductor wafer was ground and the tape was peeled off. All of fifty
wafers could be encased without causing breakage. The time required from the beginning
of the grinding to encasing was 160 minutes. The results are shown in Table 1.
Example 3
[0059] In the same manner as that described in Example 1, the semiconductor wafer was ground
and the adhesive tape was peeled off. Furthermore, the wafer was washed with pure
water with rotating at a rotational speed of 1000 rpm for 3 minutes, dried at 3000
rpm and then taken out. All of fifty wafers could be encased without causing breakage.
The time required from the beginning of the grinding to encasing was 160 minutes.
The surface contamination of the encased 8 inch mirror wafer was measured by the above
procedure. The results are shown in Table 1.
Example 4
[0060] In the same manner as that described in Example 3, except that a mirror wafer having
a bore diameter of 6 inch and a thickness of 600 µm was used and the thickness after
rough grinding was adjusted to 150 µm and the thickness after finish grinding was
adjusted to 80 µm, the semiconductor wafer was ground and then peeling of the adhesive
tape and washing of the wafer were performed. As a result, all of fifty wafers could
be encased without causing breakage. The time required from the beginning of the grinding
to encasing was 160 minutes. The results are shown in Table 1.
Comparative Example 1
[0061] In the same manner as that described in Example 1, except that one surface of the
unstretched EVA film having a thickness of 120 µm was subjected to a corona discharge
treatment, thereby adjusting the surface tension to 50 dyne/cm, and this film was
used as a base film, an adhesive tape was obtained. The resulting adhesive tape was
applied on the surface of fifty mirror wafers having a diameter of 8 inch and a thickness
of 700 µm and then fed to a back surface grinding machine. In the back surface grinding
machine, rough grinding and finish grinding were carried out in the same manner as
that described in Example 1. Then, the back surface was washed and dried and the resulting
wafer was encased in the cassette.
[0062] Then, the cassette was fed to an adhesive tape peeling device, where the tape was
peeled off. Two wafers were broken by contacting with a encasing port of the cassette
when the wafers are taken out from the back surface grinding machine and then encased
in the cassette. Furthermore, one wafer was broken when the wafer was fixed to the
chuck table before peeling off the tape in the adhesive tape peeling device, and four
wafers were broken in case of tape peeling. The time required from the beginning of
the grinding to encasing after peeling of the tape was 190 minutes. The results are
shown in Table 1.
Comparative Example 2
[0063] In the same manner as that described in Comparative Example 1, the semiconductor
wafer was ground and the tape was peeled off. Furthermore, the wafer was fed to the
washing step and preliminary washing and proper washing were performed for 3 minutes
and 5 minutes, respectively, in a cassette type overflow washing tank. Then, the wafer
was dried by using a rotary drier. Two wafers were broken by contacting with a encasing
port of the cassette when the wafers are taken out from the back surface grinding
machine and then encased in the cassette. Furthermore, one wafer was broken when the
wafer was fixed to the chuck table before peeling off the tape in the device for peeling
an adhesive tape for semiconductor surface protection, and two wafers were broken
in case of tape peeling. The time required from the beginning of the grinding to encasing
after tape peeling was 190 minutes. Furthermore, one wafer was broken in case of transferring
to the washing step. The time required from the beginning of the grinding to the completion
of washing was 220 minutes. The surface contamination of the encased 8 inch mirror
wafer was measured. The results are shown in Table 1.
